Generally, to administer certain types of pharmaceutical therapies to a neurological site, surgeons must perform repeated neurosurgeries. Specifically, the neurosurgeon must repeatedly localize the desired target site in the brain using stereotactic procedures. Stereotactic surgery is achieved by attaching a light weight metal superstructure to the patient's head to provide a fixed frame of reference for insertion of electrodes, probes, instruments or other medical devices into the brain. The apparatus provides multiple degrees of freedom in space for adjusting the positioning of the medical device to be inserted into the brain. Therefore as the patient's head moves in space the metal superstructure also moves in a one to one correspondence. However, the electrode, probe or device to be inserted into the patient's brain is immobilized with respect to the superstructure and therefore always remains in the same position relative to the head or brain. Hence, the stereotactic frame serves as a platform whereby an instrument is guided to a desired brain target site using stereotactic coordinates. That is, pre-mapped brain coordinates are used that are set on the superstructure. The positioning of the target site with respect to the metal frame is verified with imaging techniques, such as CT or MRI images. From this known relationship, the stereotactic coordinates are determined for positioning the probe in the target site. In addition, other techniques are also used to verify the target site area, such as using stimulation or recording electrodes. For example, the target site or nearby adjacent areas can be stimulated with a stimulation electrode for determining appropriate neurophysiological responses. In other situations, a recording electrode can be used to sample neuronal activity to confirm target site location. Once the instrument is guided to the desired target, treatment can begin, such as the administration of a biologic, chemical or pharmaceutical substance to the target site.
The above techniques and procedures are used for each surgical operation. However, repeated intermittent application of pharmaceutical agents to the same target site over time (such as days, weeks, months, etc.) would require many neurosurgical operations. Besides the known risks of multiple repeated operations, there are a number of other difficulties and risks to the patient. Repeated neurosurgical procedures can result in sub-optimal placement of the instrument with respect to the target site that may lead to significant morbidities or failure of the treatment. Sub-optimal placement may result from brain shifts during the operative procedure, changes in tissue pressure or consistency with repeated penetrations of the instrument, deflection of the instrument as it passes through previously penetrated brain tissue to the desired target or may result from miscalculation of stereotactic coordinates.
Additionally, repeated stereotactic neurosurgery may result in damage to the target site. Damage to a target site or region of interest is harmful to the patient's brain tissue and may necessitate a relocation of the target point. Hence, delivery of a biologic, chemical, or pharmaceutical without the need for repeated stereotactic neurosurgery or additional stereotactic apparatuses is greatly desired for such therapies.
Another problem associated with current devices is the delivery of pharmaceuticals to patients that may over-extend the target area. Over-extension and into and beyond the target site may cause damage to the patient's surrounding brain tissue and potentially cause a corresponding functional loss. Therefore, a delivery system that precisely targets the area of interest without over-extending the delivery site is important for patient safety.
Several prior art apparatuses allow for the introduction of drugs or therapeutic agents to selected brain tissue sites. U.S. Patent Application Publication No. 2004/0215164 A1 discloses a catheter assembly for intracranial treatments. This device is not chronically implantable, nor does this device prevent over-extension into the delivery site. Tissue or fluid accumulation at the target area can interfere with precise delivery of pre-determined amounts of substances. Another prior art device is described in U.S. Pat. No. 5,800,390. This patent discloses an intracranial tube for delivery of a pharmaceutical. Similarly, this device also does not prevent overshooting or over-extension into the delivery site.
Another prior art device is described in U.S. Patent Application Publication No. 2004/0186422. This application discloses an apparatus for delivering therapeutic or diagnostic agents to a target site within tissue. However, this device is also not chronically implantable, nor does this device prevent over-extension into the delivery site.
It is therefore desirable to provide a therapy delivery system that is chronically implantable to prevent damage to the target site for intermittent repeated surgeries, and which also prevents overshooting or over-extension into the delivery site.